Various measures have been developed for discovering lost articles or lost persons and determining the locations thereof, and systems have been developed and put to use with attention to the efficiency, speed, accuracy and reliability of determining the locations of lost articles and lost persons. Particularly as regards finding lost persons in mountain rescue operations and similar, a system that excels in flexibility and efficiency is required because the region searched is extremely expansive and rapid reliable discovery is essential.
JP2005-229449A, for example, teaches a technology related to a system for determining the position of a lost person. According to the disclosed technology, mountain climbers carry small transmitters functionally capable of transmitting multiple radio waves, and a lost climber is discovered by conducting a first search from the air by helicopter or the like relying on transmitted VHF-UHF band radio waves that travel long distances, where after a ground search team provided with distress area information through a distress relief center approaches the distress site and conducts a second search using MF band or MF band plus VHF-UHF band radio waves. It is suggested that this technology can help to rescue a disaster victim buried in snow, such as by an avalanche, because it enables quick determination of the victim's location.
This technology does in fact make it possible to grasp a disaster victim's whereabouts. However, with the disclosed system, since high-accuracy determination of a lost person's position is extremely difficult, the search has to be conducted based on very vague position information, so that a major problem emerges of the search team, among others, being exposed to the risk of a secondary disaster. Another intrinsic and fatal problem is that in a terrain that blocks radio wave propagation, even ascertaining the presence of the disaster victim may become impossible. In addition, the first search has a problem of poor efficiency because it is conducted solely by a helicopter or similar.
Moreover, JP2002-342858A teaches a technology related to a system wherein a discovery assist device carried by a sought person transmits current position information, an information management device detects distress possibility based on an activity plan, and sought person current position information is acquired from the discovery assist device and provided to a searcher, whereby search activity is supported, and when position information cannot be acquired from the discovery assist device, search activity is supported by guiding a mobile radio repeater and acquiring position information from the discovery assist device. It is suggested that when a possibility of distress arises, a rapid and suitable alert enables an efficient search to be conducted.
Although this technology might enable discovery of a sought person even in a case where current position information for the sought person cannot be acquired from the discovery assist device, it does not ensure rapid discovery of the sought person because if no activity plan of the sought person is available, it is very difficult to suitably guide the mobile radio repeater.
A need is therefore felt for a search and rescue system that can easily and accurately grasp existence of a lost article or lost person, and when the lost article or lost person is discovered, can calculate position of the lost article or lost person with high accuracy and rapidly determine and communicate its location.    Patent Document 1:
JP2005-229449A    Patent Document 2:
JP2002-342858A